In general, a speed-up device is employed in the conventional art for a liquid crystal panel having 480 data lines so as to display a video signal of an NTSC system having 240 data lines.
FIG. 1 is a block diagram showing the construction of a conventional liquid crystal display for displaying a video signal on a liquid crystal panel by using the speed-up device, and FIG. 2 is a detailed view showing the construction of the speed-up device as shown in FIG. 1.
A large-sized LCD module can exhibit a resolution at or above the VGA level, which is much greater than the 240 data lines per field for NTSC system video signals. Therefore, as shown in FIG. 1, the liquid crystal panel employs a speed-up device so as to display an image data on a TFT-LCD panel having 480 data lines.
In FIG. 2, the speed-up device of FIG. 1 comprises two line memories 1 and 2 and a memory controller 3. The memory controller 3 generates a control signal to process entered R, G and B signals at an increased speed. With this speed-up device, signals of 480 data lines are synchronously displayed on the LCD panel.
FIG. 3 is a timing diagram illustrating the operation of the conventional speed-up device. In FIG. 3, the whole 480 lines may be displayed on the LCD panel within the same time period required for the 240 lines of the NTSC signal by processing R, G, and B signals into R', G' and B' at an increased speed.
To display signals of 480 data lines without the above-described speed-up device, another method has been utilized where a gate driver IC is redesigned to synchronously generate gate driving pulses for two data lines. The signal-timing diagram in this case is shown in FIG. 4.
As shown in FIG. 4, two gates are opened at the same time by corresponding gate driving pulses, e.g., G.sub.1 and G.sub.2 for 1 horizontal synchronous interval. A horizontal synchronous interval refers to an interval between the generation of horizontal synchronous signals. It is also understood that the operating frequency of the horizontal synchronous signal is identical to that of the clock signal of the gate driver IC. It may be apparent that redesigning the gate driver IC as described above appears to be as effective as the employing a speed-up device for the purpose of displaying signals of 480 data lines on the LCD panel.
However, it is known that the conventional liquid crystal display presents the several problems. First, when a speed-up device is employed, the price of the system increases because the speed-up device requires a memory and a memory controller and too much noise may occur in the system due to the usage of the memory. Second, when a gate driver IC is redesigned, the development costs for a special gate driver IC are increased and the driving ability of a source driver IC must be improved because two picture elements are turned on by each output of the source driver IC.